René Descartes was a very clever thinker. He proved his own existence, declaring that because he thought, he must exist: “I think, therefore I am.”

But the 17th century philosopher-mathematician-scientist committed a serious mental blunder when he decided that the mind doing the thinking was somehow separate from the brain it lived in. Descartes believed that thought was insubstantial, transmitted from the ether to the pineal gland, which played the role of something like a Wi-Fi receiver emb...